Chemical mechanical planarization (CMP) is an essential process in the manufacture of semiconductor chips today. Dielectric and metal layers used in chip fabrication must be made extremely flat and of precise thickness in order to pattern the sub-micron sized features that comprise a semiconductor device. During CMP, the combination of chemical etching and mechanical abrasion produces the required flat, precise surface for subsequent depositions. The polishing pad is usually made of polyurethane and has small pores to carry the slurry under the wafer. As a result of the polishing process, pad material and slurry residues collect in the pores, plugging them, and reducing the polish rate due to slurry starvation. When the pad becomes clogged, it becomes necessary to "condition" the pad to restore its full functionality. That is, the accumulated material must be removed before it completely clogs the pad and results in a smooth, glazed surface that does not effectively polish the semiconductor wafer. A nickel/chromium conditioning wheel with a surface of diamond abrasives embedded in a nickel/chromium setting alloy is used to condition the pad. The conditioning wheel is pressed against the polishing pad by a conditioning wheel actuator, e.g., a hydraulic arm, and the pad and conditioning wheel are rotated while de-ionized water is flowed to rinse away abraded material. The diamond elements remove embedded particles, slurry, and polishing by-products from the polishing pad. The conditioning proceeds until the pad is "re-surfaced" and new pores are exposed.
As the conditioning wheel is rotated against the polishing pad, the wheel, setting alloy, and the diamonds come in contact with the chemical/mechanical slurry. Conventional conditioners for an oxide polisher have useable lifetime of about 15,000 wafers. On the other hand, conventional conditioners for a tungsten metal polisher have a useable lifetime of only about 5,000 to 7,000 wafers. While nickel/chromium is generally considered a chemically-resistant alloy, the slurries used to planarize metal layers, especially tungsten, are very corrosive. As a consequence, the chemicals of the slurry attack the nickel/chromium setting alloy and, over time, loosen the diamond crystals, causing them to fall out of the polishing surface. Of course, this reduces the effective surface area of the conditioning wheel and slows the conditioning process.
Accordingly, what is needed in the art is a conditioning wheel that is highly resistive to the effects of the corrosive oxidants primarily found in metal polishing slurries.